1. Field of the Invention
The present invention relates to a radiation image information capturing apparatus for reading the radiation image information of a subject by converting the radiation image information into an electric signal, and a method of detecting the temperature of an amplifier of the radiation image information capturing apparatus.
2. Description of the Related Art
X-ray breast image capturing apparatus (mammographic apparatus) apply an X-ray radiation to a subject, i.e., a breast, to capture and record the radiation image of the subject in a radiation image recorder (solid-state detector), and read the recorded radiation image from the radiation image recorder by applying reading light from a reading light source to the radiation image recorder while moving the reading light source relatively to the radiation image recorder with a scanner to scan the radiation image recorder for thereby causing the radiation image recorder to emit light representing information depending on the recorded radiation image.
The radiation image recorder comprises a radiation solid-state detector made up of a matrix of photoelectric transducers and thin-film transistors (TFTs), and may be of the light reading type, the light conversion type, or the direction conversion type.
The radiation solid-state detector outputs an image signal in the form of an analog electric signal which represents a recorded radiation image. Since the output analog electric signal has a weak signal level, it is amplified by an amplifier.
The weak analog electric signal tends to be easily affected by temperature changes of the radiation solid-state detector and the amplifier. It is desirable to acquire radiation image information which is stable against temperature changes from the weak analog electric signal.
There is known a radiation image capturing apparatus disclosed in Japanese Laid-Open Patent Publication No. 2002-22841 (hereinafter referred to as “conventional art 1”) for acquiring an image signal that is stable against temperature changes of an amplifier. As shown in FIG. 13 of the accompanying drawings, the known radiation image capturing apparatus has a sensor substrate 1 having a matrix of pixels including photoelectric transducers and TFTs (converting means). The sensor substrate 1 is made of glass, and a fluorescent layer 2 is disposed on the sensor substrate 1.
A detecting integrated circuit IC (amplifying means) is mounted on a surface of a flexible board 3 having an end electrically connected to the sensor substrate 1 and another end electrically connected to a signal processing circuit substrate 4. A cooling fin unit 5 for radiating the heat generated by the detecting integrated circuit IC is held in contact with a heat transmitter 6 mounted on the detecting integrated circuit IC. The cooling fin unit 5 is coupled by sleeves 9 to an elastic plate 7 and a fixing plate 8 which are mounted on the opposite surface of the flexible board 3 that is remote from the detecting integrated circuit IC.
According to the conventional art 1, the cooling fin unit 5 is positioned only on the side of the surface of the flexible board 3 on which the detecting integrated circuit IC is mounted. Therefore, the heat generated by the detecting integrated circuit IC tends to flow to the sensor substrate 1 along the opposite surface of the flexible board 3 that is remote from the detecting integrated circuit IC.
Japanese Laid-Open Patent Publication No. 2000-116633 (hereinafter referred to as “conventional art 2”) discloses another radiation image capturing apparatus having a sensor substrate surrounded by a flexible circuit board. Upper and lower shield members are mounted respectively on upper and lower surfaces of the flexible circuit board with upper and lower heat insulators interposed therebetween. The lower shield member has a lower surface held against an inner frame, and the upper shield member has an upper surface held against an outer frame having a large volume.
According to the conventional art 2, the flexible circuit board is vertically sandwiched by the upper and lower shield members. Heat from an amplifying means is not prevented from being transferred through the flexible circuit board to the sensor substrate.
Japanese Laid-Open Patent Publication No. 2000-37374 (hereinafter referred to as “conventional art 3”) discloses still another radiation image capturing apparatus. As shown in FIG. 14 of the accompanying drawings, the disclosed radiation image capturing apparatus has an image capturing device 2a vertically movably supported on a mount base 1a. The image capturing device 2a includes a two-dimensional radiation detector 3a and a signal converter 4a for converting a signal from the two-dimensional radiation detector 3a into an image signal. The two-dimensional radiation detector 3a and the signal converter 4a are arranged successively from an X-ray tube, not shown.
A fan 5a as a cooling means is mounted in an upper end of the image capturing device 2a. An external air inlet port 2b is defined in a lower end of the image capturing device 2a. The signal converter 4a is electrically connected by a cable 6a to an image processor 8a and a power supply 9a in a controller 7a. 
The controller 7a, which accommodates the image processor 8a and the power supply 9a therein, is positioned outside of the image capturing device 2a. Therefore, the image capturing device 2a is small in size, and the two-dimensional radiation detector 3a is effectively cooled by the fan 5a. 
According to the conventional art 3, however, since external air is directly introduced from the external air inlet port 2b into the image capturing device 2a by the fan 5a, the temperature of a coolant, i.e., air, in the image capturing device 2a depends on the ambient temperature around the image capturing device 2a. Consequently, the temperature of the coolant drawn into the image capturing device 2a tends to vary, and the temperature in the image capturing device 2a cannot be controlled to a nicety.
In addition, the power supply 9a, which includes a power supply unit for the signal converter 4a, is disposed outside of and spaced from the image capturing device 2a. As a result, the power transmission path along the cable 6a from the power supply 9a to the signal converter 4a is long enough to pick up external noise.